GATE RECESSING OPTIMIZATION OF GAAS AL0.22GA0.78AS HETEROJUNCTION FIELD-EFFECT TRANSISTOR USING CITRIC-ACID HYDROGEN-PEROXIDE AMMONIUM HYDROXIDE FOR POWER APPLICATIONS/

The etching characteristics of GaAs and Al0.22Ga0.78As in citric acid/ hydrogen peroxide/ammonium hydroxide etching solution were studied. Th e selectivity of GaAs to Al0.22Ga0.78As was as high as 200 at 20 degre es C (510 at 0 degrees C) by optimizing the pH and citric acid/hydroge n peroxide ratio. To our knowledge, this is the best result. The etch rate of GaAs is 1000 Angstrom/min and permits a good control of the et ched depth. The effects of the etching solution temperature and the do ping level of GaAs on the selectivity were determined. The solution st ability study over the time proves that the process is very reliable. This wet etching was applied to the gate recess etching of a heterojun ction field effect transistor (HFET). Observations and measurements by electron beam microscopy are presented for short gate lengths. They s how a very good surface morphology and that the gate recess width is i ndependent of the gate length. It only depends on the etching time. Th e breakdown voltage value can be adjusted by the gate recess width. Th e possibilities of this wet etching are consequently demonstrated to b e particularly appropriate to the realization of millimeter power HFET s. (C) 1998 American Vacuum Society.